In the 3rd Generation (3G) and Beyond 3rd Generation (B3G) mobile communication systems, the coverage area of a cell is typically an important metric index of a radio access system which typically covers a radio service area through an eNodeB or an access point. However a user equipment may be located outside the service area due to mobility of the user equipment and consequently fails to access a radio access service, and even if the user equipment is located within the service area, transmission of a signal may be obscured by an obstacle on a transmission path, thereby degrading the quality of the service. For this reasons and in order to address seamless coverage of the service area and an increased system capacity at a as low cost as possible, the technology of “relay” has been proposed in a technical solution of future (3G LTE) mobile communication so that a signal can be relayed through a Relay Node (RN) or a Relay Station (RS) when the user equipment is located outside the service area or the quality of the signal can not be satisfactory to thereby extend the service area or to improve the reliability of transmission for the purpose of extending the coverage area and the capacity of a cell.
Reference is made to FIG. 1 illustrating a topology diagram of an access network of a mobile communication system with a Relay Station (RS), where a User Equipment (UE) can communicate with the side of a core network directly through an eNodeB, and when the UE is located outside a coverage area of the eNodeB or can not communicate with the eNodeB because a radio transmission link between the UE and the eNodeB is obscured by an obstacle, the UE can communicate with the eNode B through the RS relaying a signal, so that the UE can communicate with the eNodeB even in the foregoing situations for the purpose of extending the coverage area and the capacity of a cell. Particularly an air interface between the UE and the RS is a Uu interface and an air interface between the RS and the eNodeB is a Un interface.
At present, how to improve the throughput of the Un interface and to enhance a delay characteristic of the Un interface as a general performance index of a Un interface design has also become an issue under discussion and to be addressed in the industry.